Hetero Acoustic Layer Surface Acoustic Wave Resonator Composed of LiNbO₃ and Quartz

In this work, a shear-horizontal (SH) mode surface acoustic wave (SAW) resonator based on LiNbO3 (LN)/Quartz (Qz) hetero acoustic layer (HAL) structure was studied by simulation and experiment. By this HAL structure, the displacement and electric displacement are well confined in the piezoelectric layer. A lower mechanical loss of Qz than that of lossy amorphous SiO2 further enhances the quality ( Q ) factor. In addition, a negative temperature coefficient of frequency (TCF) of LN is compensated by selecting the crystalline orientation of Qz with a positive TCF. According to simulation results, the Euler angles of (0°, 101°, and 0°) and the normalized thickness of 0.2-0.3 λ (wavelength) for LN are selected to obtain a higher impedance ratio ( Z -ratio) and bandwidth (BW). The Euler angles of (0°, 160°, and 90°) for Qz are selected to obtain the positive maximum TCF. The fabricated resonator exhibits a Z -ratio of 95 dB and a BW of 15.9% in the 700 MHz range. The fit figure of merit (FoM) reaches 410, which is the best level ever reported for an LN-based resonator. The TCF of the resonator is -77 ppm/°C at anti-resonance frequency. A group of resonators composed of LN and LN/Qz with thin and thick electrodes were fabricated to further illustrate the good performance of LN/Qz. The LN/Qz HAL SAW resonator demonstrated in this work exhibits a high Z -ratio, low TCF, and wideband, which has the potential for high-performance wideband filters with steep passband and good temperature characteristics.